Process for overcoming water blocking of a petroleum producing well



United States Patent Process FOR OVERCOMING WATER: nrflocxuwe OF'A PETRGLEUMPRODUCINGTWELL Raw. settlers;qr.gaaimr L; Drapenand w s a. IenIts, mules; flkla, assigno'r's to" Essa Research a'n'd Engineering-Companwa corporation of Delaware Noll rawiiig. Application August. -3 1 95 4 Serial Nb; 447,577

v This invention concerns a novel. process for overcoming the'diificulties caused by so-callediwat'er blocking of petroleum production wells. Theinvention employsra high. vapor-1 pressure; normally gaseous, water-soluble, agent-which 'is injected-into .the reservoir througlrtth'e PI'OdUCl'lOIll well in liquid phasecondition. fI'hereafter the pressure required to:inject-this agentiintotthe reservoir 4 r must flow from a considerable volume of the reservoir into any givenproduction.well; .Inview.ofthisfunneling of oil into the production well it is apparent that the resistance to flow in the immediate vicinityof a production well necessarily constitutes a real bottleneck.

One? of-the problems which aggravates productionaof oil is known as water blocking. In general terms twater blocking-;is a condition resulting-from'the presenceiof water within the pores of the producing formation in the immediate vicinity of a production well. Presence of water at this location sharply reduces the permeability to oil in the critical flow region at the production well. In the case of water-wet sands, after prolonged oil production flow of oil through the sands may gradually displace the water so as to return the sand to nearly its original permeability to oil. However this is often a very long process and limits the amount of oil which can be produced during the initial phases of production. Again in the case of oil wet sands, part of the permeabil itiy to oil is ordinarily permanently lost due to water blocking. It is consequently the principal purpose of this invention to provide a rapid and effective remedial treatment for conditioning the reservoir in the vicinity of a production Well so as to overcome the problem of water blocking.

In accordance with this invention, an agent is injected into the reservoir adjacent the production well. The agent to be injected must be forced into the reservoir in liquid phase although it is essential for the purposes of this invention that the agent be normaly gaseous and that it have a high vapor pressure. It is also the particular feature of this invention to employ an agent which is readily absorbed by water. For the purposes of this invention the material which is best adapted to supply the required properties is ammonia. Ammonia has a relatively high critical temperature so that it can be liquefied at the temperature conditions existent in a reservoir. The pressures required to liquefy the ammonia are in the range of about 200 to 1000 lbs. per sq. in. at ordinary crude oil reservoir temperatures. These pressures may be readily attained by using conventional injection compressors. Ammonia is readily absorbed by water in very Substantial amounts. This absorption of the ammonia 2,776,714 Patented Jan. 8, 1957 by water. aidsin the elimination of water blocking'intwo Ways: first of all absorptionof ammonia by water results inan enormousrincreasedn the volume of theaqueous solution. As a-.result, thist essentially serves to expand thetwaterrso asto' force'the water from small capillaries in. which ill. maybe trapped. .Secondly,-after absorption of ammonia in watentby releasing the pressuremaintained at theip-roductionrwell', vaporization of ammonia-occurs in amanner'forcingwater through. the reservoir toward .tlie production.well." For these reasons the present invention is. particularly concerned;with theause of ammonia as aunique injection agent for treatinga producing well to-overcome'waterblock-ing At thetsame time,-it is contemplatedzthatother liquefiable-gases having high .vaponpre ssures can. be employedto obtain at, least: some of the-benefits ofthis invention.

The: amount; of ammonia required in the treatment of a' producingzwell-to secure the benefits of-this invention a relatively small amount; In general-conditionsof water blocking create a critical bottleneck at the produc- .tion welhfor'aaradius of only aboutS-to 5-. ft; around the bore. hole..-..Becauseof this considerationn relatively small. amounts of ammonia are required in order to secure'thetnecessary removal of water in this restrictedreg i on. In-gene-ral it ;is contemplated that aboutone barrel of liquefied ammonia'isto: be-used-pcr line'arwft, of sand corresponding tto the thickness of theproducing formation at the production well. For example, in conditioning'a, 'production well. penetrating El-VPFOdllClTlEJfOI'IHQtiOH having.ajhicknessof:about! 20 ft.,' approximately-20 bbls. Qfa-mmOnia-are required: I It is'appare'nt that somewhat greater quantities of ammonia'can be employed although 5.6 of substanitally greater quantities is' economieallyiun- .justifieda. I ,7 In thetpractice. of this invention as. the-first stepxof the operatiom. a. slug. or bank of liquid-ammonia is: injected into? a. produ'etionwell at a suitablerpressureto maintain the ammoniain-liquid phase during injection; N

This treatment can preferably be applied to a production well immediately after the well has been completed so as to eliminate water in the producing formation caused by water invasion during drilling and completion of the well. A convenient technique for injecting the ammonia is to first pump the ammonia into the production well at any desired pressure and to thereafter pump a fiuid such as natural gas after the ammonia at a pressure of about 1000 lbs. per sq. in Injection of the natural gas following the ammonia serves to ensure liquefaction of the ammonia and serves to force the liquefied ammonia outwardly from the production well into the producing formation in the immediate vicinity of the production well. In the practice of this invention it is probable that the initial injection of liquid ammonia serves to displace a portion of the water in the water blocked area so as to force the water away from the bore hole. This effect aids in minimizing the Water blocking condition although a more important effect is secured by the absorption of ammonia in the water adjacent the bore hole. This absorption of ammonia is accompanied by a very great increase in the volume of water traped in the pores of the producing formation. Since most of the water is retained in many cases by minute capillaries in the producing formation, this expansion causes water to be forced from the smallest capillaries. These phenomena occur during injection of the ammonia while the ammonia is being forced through the producing formation immediately adjacent the production well.

It is preferred that sufficient drive gas, such as natural gas, be injected so as to drive the liquid ammonia from the immediate vicinity of the bore hole for a distance of about 5 to 10 ft. from the bore hole. Effective dis placement of the ammonia can be secured in driving it for this distance so that the ammonia can exist as a substantially unitary band or pool about the bore hole.

In the final step of this process the high pressure maintained at the production well during injection of the ammonia is released so that pressure at the bore hole is dropped to substantially atmospheric pressure.

The manner in which pressure is released after injection of the ammonia is an important feature of this invention. In the case of a reservoir having a relatively high natural pressure, it is particularly desirable to gradually release pressure at the production well to secure flow of the aqueous ammonia solution with a minimum of ammonia vaporization. This serves to remove the greatest proportion of water from the reservoir while obtaining the full benefit of the swelling properties of ammonia referred to. This technique can be employed when the pressure existent in the reservoir is of about the magnitude required to maintain the ammonia in liquid phase in the reservoir. However, for reservoirs having relav tively low pressures this technique cannot be employed since vaporization and diffusion of the ammonia into the reservoir would result. In this case, then, it is more desirable to sharply release the pressure at the production Well.

This results in imposition of a substantial pressure differential between the band of liquid ammonia and the bore hole. Ammonia will be virtually flashed to gas phase causing rapid flow of ammonia through the volume of the reservoir immediately adjacent the production well. This results in sweeping residual water from the vicinity of the well bore so as to substantially eliminate the water blocking.

As described therefore, the present invention concerns the injection of liquid ammonia into the reservoir adjacent a production well. By the mechanism described, the subsequent flow of ammonia into the production well physically displaces the water present. It should be observed that this technique not only serves to materially improve productivity of a Well bore by eliminating conditions of water blocking, but also by causing a decrease in the connate water content of the formation adjacent the bore hole.

Substantially complete recovery of the injected ammonia can be achieved, by pumping the bore hole so as to recover the injected ammonnia. Alternatively residual ammonia and expelled water will be produced from the bore hole as production of crude oil from the well is initiated.

What is claimed is:

1. A process for increasing the productivity of a waterblocked petroleum well penetrating a producing formation comprising injecting liquid ammonia through the Well into the producing formation in the immediate vicinity of the well, applying pressure to the producing formation to maintain the ammonia in liquid phase and to force the ammonia into the formation, thereafter releasing pressure at the well to cause etllux of the injected ammonia, and recovering ammonia, crude oil and water from the formation through the well.

2. The process defined by claim 1 in which about one barrel of liquid ammonia is injected per linear foot of the thickness of the producing formation.

3. Process defined by claim 1 in which the said liquid ammonia is injected at pressures in the range of about 200 to 1000 lbs. per sq. in.

4. A process for improving the productivity of a waterblocked petroleum well comprising the steps of: injecting a bank of liquid ammonia at a pressure of about 200 to 1000 p. s. i., thereafter injecting an inert gas at a pressure of about 1000 lbs. per sq. in. to force the bank of liquid ammonia for a distance of about 5 to 10 ft. into the pro ducing formation about the well, and finally releasing pressure at the well and recovering ammonia, water and crude oil from the said well.

5. The process defined by claim 4 in which the natural pressure in the reservoir is substantially that required to maintain the ammonia in liquid phase and the pressure is gradually released at the well.

References Cited in the file of this patent UNITED STATES PATENTS 949,567 Flanegin Feb. 15, 1910 1,954,973 Zaniboni Apr. 17, 1934 2,241,253 Garrison May 6, 1941 2,379,561 Bennett July 3, 1945 

1. A PROCESS FOR INCREASING THE PRODUCTIVITY OF A WATERBLOCKED PETROLEUM WELL PENETRATING A PRODUCING FORMATION COMPRISING INJECTING LIQUID AMMONIA THROUGH THE WELL INTO THE PRODUCING FORMATION IN THE IMMEDIATE VICINITY OF THE WELL, APPLYING PRESSURE TO THE PRODUCING FORMATION TO MAINTAIN THE AMMONIA IN LIQUID PHASE AND TO FORCE THE AMMONIA INTO THE FORMATION, THEREAFTER RELEASING PRESSURE AT THE WELL TO CAUSE EFFLUX OF THE INJECTED AMMONIA, AND RECOVERING AMMONIA, CRUDE OIL AND WATER FROM THE FORMATION THROUGH THE WELL. 